With the development of the Internet network, huge multimedia services take emergence, and people's needs on mobile communication are not limited to telephone and message services any more. Currently, application services are introduced into the multimedia services and have a feature that multiple users can receive the same data at the same time, for example, video on demand, television broadcast, video conference, online education, interactive game, etc.
An MBMS (Multimedia Broadcast Multicast Service) technology is put forward to use resources of a mobile network effectively. The MBMS is a point-to-multipoint service that one data source transmits data to multiple users, and network resources can be shared through this service, including sharing resources of a mobile core network and an access network, especially sharing air interface resources, moreover, the MBMS in 3GPP can realize not only multicast and broadcast of message-type services of pure-text and low-rate, but also multicast and broadcast of multimedia services of high-rate.
Since the MBMS service is a service directed to the whole network, a same MBMS service may be established at different lower layer network element nodes. FIG. 1 is a flow chart of a method for synchronization processing of a MBMS service of multiple network elements in the prior art, which comprises the following processing.
Step S102, an upper layer network element transmits MBMS service data packet(s) to respective lower layer network elements, and the service data packet(s) bears service data and carries timestamp information, data packet sequence number information, accumulated service data length information, etc. The upper layer network element marks one or more consecutive service data packets with same timestamp information, and the data packets marked with the same timestamp make up of a data burst or are referred to as a synchronization sequence. Specially, the upper layer network element marks each service data packet as one data burst or synchronization sequence, and here each data burst or synchronization sequence only includes one service data packet.
Step S104, the lower layer network elements need to perform an RLC (Radio Link Control) protocol layer concatenation processing on the service data carried by the service data packet(s) in a same data burst, and the RLC concatenation processing will not be performed on the service data packet(s) of different synchronization sequences. Moreover, while performing the RLC protocol layer processing on the data packet(s) of one synchronization sequence, a reset processing is performed, starting from the first data packet of each synchronization sequence, on an RLC sequence number of an RLC protocol layer. That is to say, starting from the first RLC PDU (Protocol Data Unit) of the first data packet of each synchronization sequence, the RLC sequence number is assigned from a certain agreed or configured fixed value. The advantage of such performance is as follows: when it occurs that multiple consecutive data packets are lost during a transmission process from the upper layer network element to the lower layer network element, the lower layer network element cannot determine according to the prior art the length of the RLC PDU occupied by the lost data packets during the performance of the RLC processing, which results in that the network element which loses packets cannot keep consistency in subsequent RLC processing with the other network elements, while this problem can be avoided by resetting the RLC sequence number at the beginning of each synchronization sequence, and this can ensure that the RLC sequence numbers of respective network elements are consistent with one another at the beginning of each synchronization sequence.
S106, for service data carried by service data packets marked by the timestamp in the same synchronization sequence, the lower layer network elements sequentially transmit, at wireless interfaces, the service data packets from a transmitting time point corresponding to the timestamp, since the above information transmitted by the upper layer network element to the respective lower layer network elements is completely consistent with each other, the respective lower layer network elements can perform completely consistent processing, thereby realizing synchronously transmitting of the MBMS service among cells of the respective lower layer network elements.
Currently, the timestamp information of each data packet can be set in the following two manners.
Manner 1: the upper layer network element marks a timestamp according to the time when it receives the service data packets, and service data packets received within a time interval with a specific length are marked with the same timestamp, wherein the time interval with the specific length is called as a synchronization sequence length, or a scheduling period.
Manner 2: the upper layer network element virtualizes the RLC protocol layer processing of the lower layer network elements, and marks the service data packets on which the RLC concatenation processing should be performed with the same timestamp according to the result of the virtualized RLC processing.
In the above two setting manners, as the timestamp information depends on the time when the service data packets arrive at the upper layer network element, the timestamp intervals of the service data packets cannot be determined. Suppose the service data flow received by the upper layer network element is a data flow shaped according to a service QoS, that is, within a random period of time, the bandwidth of the service data flow does not exceed a maximum bandwidth defined by a service QoS parameter, and suppose the channel resources of the wireless interface within the period of time matches the QoS parameter.
One MBMS service can be transmitted at wireless interfaces in a TDM (Time Division Multiplexing) manner, and the TDM configuration comprises the following parameters: a TDM period, a TDM offset and a TDM repeat length. Available TDM resources of one service can be represented as follows: (a system frame number CFN dividing exactly the number of 10 ms radio frames included in a TTI (Transmission Time Interval)) modular operation (TDM period)=TDM offset+i, i=0, 1, . . . , (TDM period−1). Specifically, one MBMS service is transmitted, within a TDM period it is allocated, from the (TDM offset)th TTI and within consecutive scheduling TTIs (transmission time interval) in a number of TDM repeat length, wherein the TDM repeat period is no more than 9, and the length of the TTI that can be used by the MBMS service is 40 or 80 ms. One service can only be transmitted at the wireless interface within a configured available transmission time in the TDM period.
When data are transmitted in manner of TDM, as the transmission time of one MBMS service at the wireless interface is not consecutive, but appears periodically and circularly according to the configuration of the TDM, due to current scheduling methods, the timestamp is uncertain, and thus the timestamp information may not directly correspond to a start time when the MBMS service can be transmitted at the wireless interface. That is, the timestamp and the transmission opportunities (available transmission time) of the wireless interface cannot correspond to each other one by one, for example, as shown in FIG. 2, the synchronization sequence length does not match the TDM period.
FIG. 3 is a schematic view of inconsistent allocation of resources corresponding to different synchronization sequence lengths. As shown in FIG. 3, in the TDM configuration manner, as its wireless channel resources are not consecutive, within the same period at different positions, available wireless resources are different, and in this situation, the scheduling algorithms in the prior art will result in an error result. The scheduling algorithms in the prior art suppose that service data packets that can be transmitted in a certain period may not be able to be transmitted at the wireless interface and then a situation of overflow appears, which will result in loss of service data and reduce service receipt quality seriously.